The present invention generally relates to the production of articles of manufacture in a computer simulation or in the real world, and more particularly, to a method and system for accurately evaluating part-to-part fit up between two or more simulated or manufactured articles.
Throughout the disclosure, and in the claims, the term “manufactured” (as in a “manufactured” article, pattern, or feature) without a modifier is used in broad sense to denote either actually manufactured (manufactured in the real world) or simulated (determined by simulation data).
American, Canadian, German, and International Organization for Standardization (ISO) standards define methods for specifying multiple levels of pattern and feature related tolerances often referred to as composite positional tolerances. Composite positional tolerances include a pattern locating tolerance and a feature relating tolerance. A pattern locating tolerance is a tolerance that relates a collection of manufactured features on an object relative individually to the specified datums of the designed pattern. A feature relating tolerance can be a tolerance that is linked to the size of a feature, that controls the positions of a set of features relative to each other, and/or controls the rotation of a pattern of features relative to a specified origin.
A tolerance specification may be applicable at maximum material condition (MMC) or least material condition (LMC). MMC may be defined as the condition in which a feature of size contains the maximum amount of material within the stated limits of size, for example, minimum hole diameter or maximum shaft diameter. LMC may be defined as the condition in which a feature of size contains the least amount of material within the stated limits of size, for example, maximum hole diameter, or minimum shaft diameter. An allowable tolerance may be specified as the combination of the feature-relating tolerances and the departure from a material condition.
With reference to FIG. 1, one method for documenting inspection data consists of paper gauging in which information is recorded on paper. Measurements are taken and errors are plotted on a grid 94 at an enlarged scale using a true position 96 as the origin. Hole positions 92 are then plotted on the grid 94. Concentric circles 90 representing tolerance zone diameters are then overlaid to determine positional errors. This method is time consuming because it is not automated, and it is not used with an automated process. Another problem with the method is the difficulty of best fitting the concentric circles 90 into a position that encompasses all the hole positions 92 within the applicable concentric circle.
Another method for documenting inspection and simulation data uses variation analysis software that assesses feature tolerances. Approximations and iterations are used that combine size, orientation, and location variations. Multiple iterations of inspecting feature size and positions are used to increase accuracy. However, using approximations reduces accuracy, and using multiple iterations causes excessive analysis time.
Variation effects from a pattern of features may be determined when performing a variation analysis of a design prior to manufacturing that design. The variation analysis software performs hundreds or thousands of simulated build cycles, and in each cycle, varies all of the parameters randomly. Assembly variation analysis that utilizes feature patterns, such as holes, for assembly is currently reliant on approximations and iterations for the assembly of parts. Such a process may introduce error, is inefficient, and requires advanced software skills for completion.
Simulating assembly moves in which position is determined by a pattern of holes or other features is a complicated task. It is usually difficult to set up with confidence and show credibility of the results. A specialist is usually required to define the move, and he or she cannot respond as quickly as desired when asked for an evaluation.
There is a need to accurately determine variation effects on patterns of features during variation analysis, and to provide a quantifiable measure of how well two parts fit (each part having a pattern of features).